Prior Art—Movable Objective Lens for Use with Microscopes
Physikinstrumente GMBH & Co. of Karlsruhe, Germany sell a movable objective lens assembly for use with microscopes. Their model P-725 scanner uses a piezoelectric element and associated drive electronics to move a microscope objective in the axial direction, thereby moving the focus nearer to or farther from a datum position. The response time for a 250 micron step is 50 ms with a 150 g load.
The axial motion response time of this apparatus is sufficient for some of the lower-speed applications described herein, however the mounting requirements of the assembly interfere with easy changing of the microscope objective during use. In addition, the scanner is limited to use with microscope objectives only.
Prior Art—Lenses with Variable Focal Length
Lenses with controllable focal length are used in the various embodiments described below. These lenses are well known to those skilled in the art of optics. A few of the types are listed here as examples of lenses that can be used. This list is not exhaustive.
In U.S. Pat. No. 4,466,703 (1984), Nishimoto teaches a variable focal length using an electro-optic effect. Another electro-optical lens is taught by Vali et al. in U.S. Pat. No. 5,212,583 (1993). Both apply distributions of electrical potentials to electro-optical materials in order to vary the focal length of a lens assembly.
In U.S. Pat. No. 4,572,616 (1986), Kowel et al. show a liquid-crystal adaptive lens system in which the index of refraction profile of a liquid crystal assembly varies the focal length of the lens. Sun et al. show another liquid crystal adaptive (variable focus) lens in U.S. Pat. No. 6,778,246 (2004) also using electrical potential to change the refraction profile of the liquid crystal.
Gelbart, in U.S. Pat. No. 6,747,806 (2004), shows an adaptive microlens. Individual elements in a micro-electromechanical system (MEMS) array of integrated stretched membrane devices are independently addressed and controlled to vary focal length.
In U.S. Pat. No. 7,675,686 (2010), Lo et al. show a fluidic adaptive lens. A flexible diaphragm separates two transparent chambers. When the diaphragm is caused to flex by changing the properties of fluids within the chambers, the focal length of the lens changes. Another fluidic variable lens is shown by Kobrin et al. in U.S. Pat. No. 7,256,943 (2007). In this patent, a fluid is contained in an elastomer membrane. A pneumatic actuator displaces the fluid and causes the shape of the membrane to change, thereby changing the focal length of the lens.
U.S. Pat. No. 7,672,059 (2010) to Batchko et al. teaches a fluidic lens with electrostatic actuation. The lens comprises an elastic capacitor section, an elastic lens section in fluid communication with the capacitor section, and a fluid capable of motion between the two. Applying a voltage to the capacitor section causes it to deform, urging the fluid to flow into or out of the lens section, causing the lens section to deform, thereby changing the focal length of the lens section.
Another fluidic lens is described in a paper by Oku and Ishikawa in Applied Physics Letters, V. 94, pages 221108-1 to 221108-3 (2009). Two separate chambers are joined by an orifice. A first fluid having a first index of refraction fills a lower chamber, a second fluid, immiscible with the first and having a different index of refraction from the first, fills an upper chamber. A piezoelectric actuator squeezes the first chamber, causing the interface between the two fluids to bulge by a predetermined amount. Since the two fluids have different indices of refraction, a lens with controllable curvature is formed in the orifice. This lens can change from one focal length to another in the order of one millisecond.
Because of their potential for high speed, one or more of such lenses is used either alone or in combination with additional lenses in the embodiments described below. If high speed is not required, the same lenses can still be used or a zoom relay lens can be fitted with a servomotor and used in place of the above lenses.
Prior Art—FIG. 1
In microscopy and telescopy, it is often desirable to record an image for later use. Thus many microscopes and telescopes are arranged to accept photographic cameras. Digital cameras for these instruments are in wide use today. Cameras can receive an image through an eyepiece port (i.e. the tube in which the eyepiece is mounted), or through a separate “trinocular tube” or port, frequently found on microscopes.
If a camera has an integral lens, an adapter is used to mount the camera on the microscope or telescope's eyepiece or its trinocular tube. Such adapters are well known to those skilled in the art of optics. These will not be discussed further here.
If the camera has no lens, a separate relay lens (RL), also called a photo-eyepiece, is used to optically couple the microscope, monocular or binocular, or telescope with the camera so that the image from the microscope, monocular or binocular, or telescope is in focus on the film or sensor plane of the camera. Many prior-art RLs are available. They have differing arrangements of internal lens elements and different optical properties such as magnification, size, optimal wavelength range, materials of manufacture and the like. RLs are well known to those skilled in the art of optics. (Hereinafter when reference is made to microscopes, monoculars, binoculars, and telescopes collectively, the term “scope” will be used.)
FIG. 1 shows a simplified, cross-sectional view of a typical RL, generally at 100. RL 100 comprises a cylindrical tube 105, one or more lenses 110 secured within tube 105 at various predetermined locations, an entrance 115, and an exit 120. Tube 105 is typically metal and roughly 25 mm in diameter, although other materials and sizes are commonly found. Many different shapes and sizes are available to fit various scope configurations. Although simple meniscus lenses are shown, most prior-art RL assemblies are more complex and may include lenses of many kinds: doublets, triplets, and so forth.
In one prior-art, wide-field imaging system, light from a scope objective (not shown) enters tube 105 at entrance 115, its optical path is modified by one or more of lenses 110, and it leaves tube 105 through exit 120. A photosensor 125 is positioned to receive the light leaving RL 100. Sensor 125 can be a line-scan sensor or an area device using CCD, CMOS, Foveon (the brand name of a particular type of sensor made by the Foveon Corporation of San Jose, Calif., USA), or any other suitable imaging technology. The size of photosensor 125 can range from 1 mm square to over 50 mm square, and can include from a few to many million pixels (picture elements). The distance from RL 100 to sensor 125 ranges from a few mm to distances greater than 20 cm.
RL 100 can be inserted in place of a scope's eyepiece, or it can be inserted into the trinocular tube of a microscope that is so-equipped.
The magnification of RL 100 and the distance between RL 100 and sensor 125 are generally predetermined so that the image from the scope's objective (not shown) fills the full area of sensor 125. In addition, when RL 100 is inserted into the trinocular port of a microscope, it is moved up or down so that the image projected onto sensor 125 is in focus when the user's view through the microscope's eyepieces is in focus. When the image as seen by both is in focus, RL 100 is secured in place with a set screw or other arrangement.
Although the prior art trinocular mounting of RL 100 is used successfully, it is not easily changed while the microscope is in use. Thus all focusing of the microscopic image on sensor 125 is done by raising and lowering the microscope's stage, or otherwise varying the distance between the objective lens and the object being viewed. In addition, microscope objectives have a very limited depth of field. Thus, in many cases, while inspecting an object the microscopist must frequently adjust the focus to see at all depths of the object.
Modern microscopy benefits greatly from the use of well-known focus stacking montage, i.e., the taking of a plurality of images at different focal distances, followed by mathematical processing and combining of the images to produce an image with an extended depth of field. This is useful when viewing subjects whose visible features lie at various depths greater than the depth of field of the objective lens in use, and also objects that are tilted or have irregular surfaces. At present, focus stacking requires the manual or semi-automatic taking of images. A first image is taken with the camera, then the focus is adjusted to present a new focal plane for taking a second image, and so forth until the entire stack is complete. This procedure takes time and requires the operator to touch the microscope, which can result in blurring of the image from motion artifacts and the like.
Binoculars and telescopes must also be adjusted to focus on near or far objects. Thus the images they gather can also benefit from focus stacking. Focusing is normally done by moving the eyepiece in an axial direction by using a rack and pinion or other arrangement. As in the case of microscopes, blurring of the image can result when refocusing for a series of images.